Method of making printing plates

ABSTRACT

The present invention relates to a method of transferring a printing image from a relief printing form to a light sensitive photographically developable printing plate, printing cylinder, or any other printing means, or a material intended for making such a printing means. Alternatively, it may be said that the present invention relates to a method of transferring a relief printing form to a printing form intended for a different method of printing, e.g., a planographic method of printing.

United States Patent Inventor Poul H. Kongstad Ljunggatan 39, Furulund, Sweden Appl. No. 736,431 Filed June 12, 1968 Patented Oct. 26, 1971 Priority June 12, 1967 Sweden 8254/67 METHOD OF MAKING PRINTING PLATES 4 Claims, 2 Drawing Figs.

US. Cl 96/33, 355/79 G03f7/02, G03b 27/02 Field of Search 96/33;

[56] References Cited FOREIGN PATENTS 663,428 5/1963 Canada 96/33 730,639 5/1955 Great Britain 96/33 Primary Examiner- Norman G. Torchin Assistant Exam bier-Alfonso T. Suro Pico Attorney-Fred C. Philpitt METHOD OF MAKING PRINTING PLATES The method according to the invention is characterized in that a print is made on a light permeable paper or other translucent or transparent material and said paper is placed with its print in a direct contact with a light sensitive photographically developable material intended for making a printing plate or another corresponding photographically developable surface and is exposed to light whereupon said photographically developable material is developed in a conventional manner.

Preferably, a minor reversed print is made, said print being placed upon the photographically developable material facing said material and in a direct contact with said'material. A nonreversed picture is obtained after exposure to light and developing, the picture being suitable for offset printing.

If it is desired to make an intermediate material, e.g., a socalled carbon tissue intended for manufacturing of an intaglio printing plate or an intaglio printing cylinder, a mirror reversed print is made in the same way, the print being placed so as to face the photographically developable material and in direct contact with such material. A nonreversed picture is obtained, which upon transfer to the intaglio printing form will be reversed as desired. When the intaglio printing form is used, it will of course produce a nonreversed print.

A reversed print may be provided by clamping the relief printing form in an offset printing press, and by inking said form using the inking device of said press. The image of the conventionally mirror reversed printing surface of the relief printing form is transferred via the offset surface of the offset printing press to the translucent paper, the print so obtained being automatically mirror reversed.

If the image of a plain printing form is to be transferred using the method according to the invention, one may employ an offset printing press intended for plain printingforms, e.g., a proofing press intended for plain offset printing plates which are bent and clamped onto a rotary printing offset press later on. The clamping table which supports the relief printing from which is intended for the normally thinner offset printing plates has to be lowered a distance corresponding to the difference between the thickness of the relief printing form and a normal offset printing form in such a way that the image surface of the relief printing form will be situated in the same horizontal plane as the printing surface of the normal planographic printing form of the press.

The invention has many advantages. One advantage is the fact that it is still possible to use conventional type composing and that it is not necessary to use the more expensive photo composing methods. The same advantage is gained if a text page produced by means of a relief printing form in a conventional manner is photographed, and the negative plate obtained is used for activating a photographically developable material intended to be transferred onto a printing form. This method known per se is however essentially moreexpensive than the method according to the present invention, since said known method requires for reproducing a book for example at least as much photographic film as the total area of the text pages of the book.

An advantage of the method according to the invention compared with conventional relief printing is the face that the necessary prints may be made in connection with a relief printing of a first edition. After said first printing, it is not necessary to save the expensive type metal. It is not necessary to make the offset printing plates before the printing of the next edition. Only the cheap mirror reversed paper prints have to be saved.

The relief printing form may be used for producing other final products. It is often an advantage to combine said prints directly with picture material made in a conventional manner using a photographic method, directly providing an offset printing plate. The handling of the pictures using such a method will be simpler as well as cheaper compared with the same handling by relief printing.

It is furthermore possible to print books or the like in a larger number of editions including a less number of books in each edition without increasing the costs of printing. Said costs may be kept lower by offset printing rather than by relief printing. Consequently, it is a great advantage to convert from relief printing to offset printing in a simple and cheap manner. Since it is possible to print editions including a less number of books, a smaller amount of money must be tied up in the stock of publishing houses.

Further advantages gained through the invention will be evident from the following in which a preferred example of the method according to the invention will be described in connection with the accompanying drawing, wherein:

FIG. 1 is a schematic illustration of an offset printing press which may be used for producing mirror reversed prints starting from a relief printing plate.

FIG. 2 shows the difference between the offset obtained by placing a paper intended to be exposed to light with the print facing the surface on which it is to be reproduced and the effeet obtained if the unprinted surface of the paper is facing said surface.

The method according to the invention preferably starts by using an offset printing press intended for plain offset printing plates in order to produce a print using a relief printing plate. In FIG. 1 a conventional offset press includes a clamping table 1 intended for clamping printing plates, a second clamping table 2 for supporting the sheets to be printed upon, an offset cylinder 3, and an inking device v.4. An offset printing press is furthermore normally provided with a damping unit, but since said unit is not necessary it is omitted in FIG. 1 in the same way as the rest of the details of the press not necessary for the understanding of the invention.

On the clamping table 1 which is vertically adjustable, as indicated by the double arrow B, a relief printing plate 5 is shown clamped. The clamping table I is adjusted in such a way that the upper printing surface of the plate 5 is situated at the same horizontal level as the upper surface of the clamping table 2. 0n said clamping table 2 a light permeable sheet of paper 6 or a similar material is shown clamped in place. The offset cylinder 3 is, as indicated by the double arrow A, movable laterally. The movement of said cylinder is preferably made in register with a corresponding movement of the inking device 4. Alternatively, they may be movable separately.

If a mirror reversed print is to be made using the mirror reversed relief printing form 5, the form 5 is inked using the inking device 4. Thereafter the ink is transferred to the offset cylinder 3 which receive an unreversed print. When said unreversed print is transferred to the paper 6, the desired mirror reversed print is obtained.

F IG. 2 shows the advantage of producing a mirror reversed print. Using such a print, the printed surface of the sheet of paper may be,'as shown at the left side of the figure, placed in a direct contact with a photographically developable light sen sitive material 7 intended to be transformed into a printing plate. In this position, the sheet may be exposed to light by means of a lamp 8 or another source of light.

If instead a normal unreversed print is made by using a normal relief printing method, the print has to be placed, as shown at the right side of FIG. 2, with its print on its upper side in order to produce an unreversed picture on the material 7. The paper has in this case been given the reference numeral 6. At the same time a light source has been given the reference numeral 8'. The dotted lines 9 and 9 show that a distorted picture is made when the text print is not placed in a direct contact with the photographically developable material 7. The distortion is increased due to the refraction of the light in the paper as shown by the dotted lines 10 and 10'. Furthermore the light is spread within the paper. Due to this fact the picture is blurred. The above drawbacks seem to have prevented previous developments similar to the present invention.

The invention is of course not restricted to the above described example but may be varied within the scope of the following claims. Thus, it is possible to start from a curved rotary relief printing form, the desired print being instead made by using a corresponding rotary offset printing press. One

drawback of such a process is, however, the fact that it may be difficult to register the printing surface of the relief printing cylinder in respect to the offset cylinder. Further, in some cases it may be suitable to keep the original relief printing form until the second edition is to be made, facilitating eventual changes. Changes are most frequently made in connection with the publishing of the second edition of a book. Later on there are few changes. Following editions may consequently be made in a simple manner by using printing forms made according to the method of the present invention. Beside the printing of books, the invention may of course be utilized for printing newspapers or other printed items. Special advantages are gained when printed text is to be mixedwith a great amount of picture material. In that case it is possible to print the total material by using an offset method.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

What is claimed is:

l. A method of transferring a printing image from a relief printing form to a light sensitive means comprising transferring the image from said relief printing form to a light permeable means to form a reversed image thereon, placing said light permeable means upon said light sensitive means with said reversed image facing said light sensitive means and in direct contact therewith, exposing said light permeable means and said light sensitive means to light, and photographically developing said light sensitive means.

2. A method as defined in claim 1 wherein said reverse image on said light permeable means is made by clamping said relief printing form in an offset printing press and inking said form, and transferring the reverse printing image from the relief printing form to the light permeable means by the offset printing surface of the press.

3. A method as defined in claim 2 wherein an ofi'set printing press is used intended for plain offset printing forms, the printing form clamping table being lowered a distance corresponding to the difierence between the thickness of the relief printing form used and a normal offset printing form so that the image of the relief printing form is positioned at the same horizontal level as the printing surface of a normal planographic printing form of the press.

4. A method as defined in claim 1 wherein prior to exposing said light sensitive means and said light permeable means to light a conventionally made photographic negative is combined with said light permeable means and said negative and said light permeable means are both exposed to light to provide the desired image on said light sensitive means.

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2. A method as defined in claim 1 wherein said reverse image on said light permeable means is made by clamping said relief printing form in an offset printing press and inking said form, and transferring the reverse printing image from the relief printing form to the light permeable means by the offset printing surface of the press.
 3. A method as defined in claim 2 wherein an offset printing press is used intended for plain offset prInting forms, the printing form clamping table being lowered a distance corresponding to the difference between the thickness of the relief printing form used and a normal offset printing form so that the image of the relief printing form is positioned at the same horizontal level as the printing surface of a normal planographic printing form of the press.
 4. A method as defined in claim 1 wherein prior to exposing said light sensitive means and said light permeable means to light a conventionally made photographic negative is combined with said light permeable means and said negative and said light permeable means are both exposed to light to provide the desired image on said light sensitive means. 